A word from Jeff, the 'Frozen Olaf' costume creator:

Halloween costume planning starts early in our household, so when Frozen came out in November of 2013, my daughter immediately knew she wanted to be Olaf for the coming Halloween, and here we are. I think Olaf is hilarious, so this was a fun build.
As usual, figuring out how to wear the character was the first challenge. With Olaf’s head shape, having my daughter look out through his eyes wasn’t going to work. Olaf usually has a big wide grin, so looking though the mouth worked well – and would give my daughter better peripheral vision while wearing it. The rest of the snowman design was pretty straight forward.
The next step was modeling Olaf’s head and making sure I got the right size. I usually start 3D modeling from scratch in Solidworks based on movie images, and then convert the Solidworks model into a papercraft model in Pepakura software. This time I was lucky enough to find a 3D Pepakura model of Olaf’s head online that was usable (thank-you Orel67). I build the papercraft prototype head using card stock, making modifications along the way so it can be worn. I also created models of the torso snowman segments.
Once everything looked like it would fit well in paper form, I started building the costume pieces out of 0.25” EVA foam, my costuming material of choice. EVA foam is a great material and can be heated and shaped, cut to size, and then glued together with hot glue. I used the paper models as templates for the foam pieces. It all sounds easy enough, but I have to say that Olaf’s head was a challenge to get just right in foam. My scrap bin was pretty big on this build.
After all the pieces were hot glued, I smoothed out and sealed all the glued edges with an adhesive caulk. In years past, I have sealed the foam surface with white glue or Mod Podge before painting, but I have always had problems with the finish cracking when flexed. Taking a cue from many EVA foam builders, this year I used Plasti-Dip spray to seal the foam, which worked great. I finished the costume with acrylic spray paint (a ton of satin white, some orange, and a little black and brown). I used an extra layer of textured spray paint for all the snow pieces (Design Master ColorTex Flurry).
With some white sweat pants, dyed brown shirt sleeves, and color matched 4-fingered gloves sewn by my wife, my daughter was set.
She loved the costume and has had a ball at all the events we have gone to. Olaf is pretty popular and my daughter eats up the attention. Now she just can’t wait for summer….